The present invention relates to a pneumatic radial tire and, more specifically, to a pneumatic radial tire to be attached to a vehicle with a suspension to which a negative camber angle is set, in which high-speed durability and driving stability can be improved.
In recent years, in order to improve driving stability of a vehicle, or in terms of trends, the number of vehicles with a suspension to which a negative camber angle is set has been increasing. Pneumatic tires are attached to such a vehicle in such a manner that upper portions of the tires are inclined inward when viewed from a front side of the vehicle.
Since the negative camber angle is provided as described above, change in the camber angle with respect to a road surface decreases in cornering, whereby proper contact to the ground can be obtained, and the cornering is stabilized. Moreover, initial turning ability (a changing rate of a direction of a vehicle front when starting to turn a steering wheel) is improved.
However, when the tire is used at the negative camber angle as described above, the ground contact pressure on a tread surface in running straight decreases in a vehicle outer side portion thereof and increases in a vehicle inner side portion thereof, thereby causing an uneven ground contact pressure distribution on the tread surface. Particularly, when the camber angle is no more than xe2x88x922 degrees, a ground contact area and ground contact pressure drastically increase in a shoulder portion on the vehicle inner side of the tread surface, and the unevenness of the ground contact pressure distribution is remarkable. As a result, there is a problem that durability in high-speed running is reduced. In addition, since the ground contact pressure in the vicinity of the shoulder portion on the vehicle inner side increases, the ground contact pressure decreases locally in the crown portion. Therefore, a problem arises that cornering limitation properties (lateral acceleration resistance) is deteriorated and the driving stability is contrarily lowered.
An object of the present invention is to provide a pneumatic radial tire to be attached to a vehicle with a suspension to which a negative camber angle is set, which is capable of improving high-speed durability and driving stability.
In order to achieve the above object, a pneumatic radial tire according to the present invention includes right and left bead portions, at least one carcass layer being laid between the bead portions, a plurality of belt layers being arranged on an outer periphery of the carcass layer in a tread portion, a tread surface of the tread portion being formed into a curved surface so that parts thereof in shoulder portion sides is tire-radially inwardly of that in a crown portion side, characterized in that, when the pneumatic radial tire is attached to a standard rim specified in JATMA with its air pressure being 180 kPa and with no load applied thereto, a tire meridian cross-sectional configuration of a tread surface portion of the tread surface on at least one side of a tire center line is arranged such that, when a position A is an intersection of the tire center line and the tread surface and a position B is an intersection of a straight line P drawn orthogonal to the tire axis from an edge of an innermost belt layer of the belt layers and the tread surface, an angle xcex1 between a straight line X connecting the positions A and B and a straight line Y drawn perpendicular to the tire center line from the position A is set in a range of 8 to 10 degrees.
According to the present invention described above, one side of the tread surface is shaped in a curved surface more slanted than that of conventional tires. Accordingly, when the pneumatic radial tire of the present invention is attached to a vehicle with a suspension to which a negative camber angle is set with the one side of the tread surface being located on the vehicle inner side, a local increase of the ground contact pressure on a shoulder portion on the one side can be suppressed, and a ground contact pressure distribution more even than before can be obtained. Therefore, high-speed durability and driving stability can be improved.